40 



CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC. 



variometer pointer P swings freely below the silver contacts S t and S 2 , just 

 clearing the ivory insulator i. The magnet plunger makes a contact de- 

 pending upon the adjustment of a clock at intervals of 2 seconds. So 

 long as both galvanometer coils are influenced by exactly the same strength 

 of current, the pointer will stand in line with and immediately below i and 

 no current passes through the recording apparatus. Any disturbance of the 

 electrical equilibrium causes the pointer P to swing either toward S x or S 2 , 

 thus completing the circuit at either the right hand or the left hand, at 



1 



FIG. 20. Diagram of galvanometer coil used in connection with record- 

 ing apparatus for resistance thermometers in the water-circuit of 

 bed calorimeter. A, anti-vibration tube; P, pointer. 



intervals of 2 seconds. The movement of the pointer away from its normal 

 position exactly beneath i to either S x on the left hand or S 2 on the right, 

 results from an inequality in the current flowing through the two coils in 

 the galvanometer. The difference in the two currents passing through these 

 coils is caused by a change in temperatures of the two thermometers in the 

 water circuit. 



THE CREEPER. 



The movement of the sliding-contact q, fig. 19, along the slide- wire J, is 

 produced by means of a special device called a creeper, consisting of a piece 

 of brass carefully fitted to a threaded steel rod some 30 centimeters long. 

 The movement of this bar along this threaded rod accomplishes two things. 



